As a couple Margaret and Robert had 4 children in Hamilton - however 2 must have died young
Elizabeth b.1832 - must have died young
Ann kelly Martin - b 1836 - Appeared on various census's but no record of what happened to her - did she marry? have kids?
Janet b.1838 - Again appears on census' but no idea of what became of her
Margaret 1841 - fails to appear in furure census' so I fear she died young.
If Margaret and Robert Martin married in 1834, daughter Elizabeth born c. 1832 is possibly James Strachan's daughter given the dates?
You have this I am sure, just for background here, the family entry in 1841:
Robert Martin 35 shoemaker b. Scotland
Margaret Martin 36 Tambourer
John Martin 10
Mary Martin 12
Ann Martin 5
Janet Martin 3
Peter Strachan 11
Margt Cunninghan 85 Pauper
Address: New Wynd Hamilton
From this list, there looks to be only two likely Martin/Harris children? You mentioned more? Given they went on to have a daughter Ann Martin, likely Ann Stachan b. 1828 died young and before the birth of Ann Martin c. 1836. Can't see an Elizabeth born c. 1832 nor a Margaret born c. 1841?
Monica